The IPInfo structure defines the initial matching criteria for a rule and includes the protocol, src address and port, destination address and port, and direction. Some of the standard strings and variables are predefined - any, HOME_NET, HTTP_SERVERS, HTTP_PORTS, etc.
typedef struct _IPInfo
{
u_int8_t protocol;
char * src_addr;
char * src_port; /* 0 for non TCP/UDP */
char direction; /* non-zero is bi-directional */
char * dst_addr;
char * dst_port; /* 0 for non TCP/UDP */
} IPInfo;
#define ANY_NET "any"
#define HOME_NET "$HOME_NET"
#define EXTERNAL_NET "$EXTERNAL_NET"
#define ANY_PORT "any"
#define HTTP_SERVERS "$HTTP_SERVERS"
#define HTTP_PORTS "$HTTP_PORTS"
#define SMTP_SERVERS "$SMTP_SERVERS"